In a supercritical Rankine cycle system and the like that uses CO2 as a refrigerant, a pressurizing device, namely a mechanical liquid pump, is used to pressurize the refrigerant, which has been liquefied in a condenser, to a supercritical pressure. The mechanical pump is driven by an external power source or part of the power obtained from the system. See for example, Japanese Laid-Open Patent Application Nos. 2003-232226 and 2004-36942, where a mechanical pump is used to pressurize and feed the refrigerant in the Rankine cycle system.
Mechanical pumps, however, induce mechanical loss resulting in a lowered cycle efficiency. Further, as mechanical pumps have moving components, reliability of the system is reduced, as well as requiring regular replacement of components. Replacing such devices operating at a high pressure accompanies great difficulties, increasing the maintenance cost. Furthermore, increased pumping power is needed to raise pressure of working fluid up to the critical pressure.
Accordingly, there remains a need for a way of pressurizing and transferring a refrigerant, such as in a Rankine cycle system, with a lower power consumption in comparison with mechanical pump, while increasing reliability thereof by using non-moving components, resulting in absence of mechanical loss. The present invention addresses this need.